Level detectors compare a voltage level of a signal with an unknown voltage level to a predetermined voltage threshold. An output signal, whose state is indicative of the relationship between the voltage level of the signal and the predetermined voltage threshold, is then provided. Level detectors are used in a variety of applications.
As one practical example of an application where a level detector can be useful, consider a Universal Serial Bus (USB) port for a laptop computer. When the USB port is empty, meaning that there is no USB device inserted into the USB port, the port can be characterized by a high-impedance or ground signal. In contrast, when a USB device (e.g., a memory stick, audio device, camera, etc.) is inserted into the USB port, the USB device delivers a predetermined voltage signature, such as a 100 mV pulse, to the USB port. To determine whether such a USB device has been inserted into the USB port, it would be ideal to use a voltage level detector with a predetermined voltage threshold of exactly 100 mV. In such a case, the level detector could compare the real-time voltage on the USB port (i.e., a signal) to the predetermined voltage threshold of 100 mV. If the voltage of the USB port is less than 100 mV, the level detector provides an output signal in a first state, which indicates no USB device is present. On the other hand, if the voltage on the USB port is equal to 100 mV, the level detector provides the output signal in a second state, which indicates a USB device is present. By evaluating the output state of the level detector, the laptop can determine whether a USB device has been inserted or not and take appropriate action. Numerous other applications are also possible for level detectors, such as wireless or wireline communication systems, automotive sensors, other bus protocols (e.g., Peripheral Component Interconnect (PCI)), among others.
Unfortunately, level detectors in some other approaches have been unable to provide precise voltage threshold comparisons.